This invention relates to an infra red (IR) reflective and/or electrically conductive layered assembly employing a metal/dielectric stack and more particularly to such an assembly which includes an energy-absorbing plastic interlayer.
Metal/dielectric stacks in windows to reflect infrared radiation while transmitting significant visible light are well known. The effect is to reduce temperature buildup from solar radiation within an area delimited by one or more of such windows. These stacks are called interference filters and comprise at least one layer of reflective metal sandwiched between reflection-suppressing or anti-reflective dielectric layers. It is likewise known to heat the metal layer by electrical conductance to provide defrost or deice and/or defog capability. Representative structures for motor vehicle windshields are disclosed in International Publication No. W088/1230 and U.S. Pat. No. 4,799,745. Such solar screening and/or electrically conductive layered assemblies are referred to in abbreviated form hereinafter as "IR reflective coating".
When IR reflective coatings are combined with glass in laminated glazings, particularly in vehicle windshields, it is desirable to include a plasticized energy-absorbing interlayer which contains polyvinyl butyral (PVB) in the assembly to absorb a blow, e.g. from the head of an occupant, from within the vehicle without penetrating the laminate. In such laminated assemblies, the PVB layer typically abuts the top layer of the IR reflective coating.
Unfortunately, after extended periods of use the strength of the bond between the IR reflective coating and PVB layer in laminated glazings has been less then desirable. As disclosed in commonly assigned, copending application Ser. No. 7/453,556, filed Dec. 20, 1989, interfacial adhesion between the PVB layer and the abutting top layer of the IR reflective coating deteriorates after prolonged exposure to light. This is addressed in such copending application by using special cap layers in the IR reflective coating chosen for their ability to adhere well to the PVB layer. Such cap layers promote adhesion to the PVB layer and usually do not otherwise function in the optical performance of the IR reflective coating. Moreover, as disclosed for example in published European Application No. 0263623, chromium oxide is commercially popular as the top layer of an IR reflective coating for contact with the PVB layer, yet, as hereinafter more fully disclosed, prior to this invention, the chromium oxide-PVB layer bond is still not optimal.
It would be desirable to further improve the stability of the bond between a chromium oxide layer of an IR reflective coating and an abutting PVB layer in a layered solar screening and/or electrically conductive laminated glazing assembly.